1. Field of the Invention
The present invention generally relates to signal communications, and more particularly, to architecture for integrating a single wire multi switch (SWM) transceiver and the legacy LNB mode into the same satellite set top box.
2. Background Information
In a satellite broadcast system, one or more satellites receive signals including audio and/or video signals from one or more earth-based transmitters. The satellite(s) amplify and rebroadcast these signals to signal receiving equipment at the dwellings of consumers via transponders that operate at specified frequencies and have prescribed bandwidths. Such a system includes an uplink transmitting portion (i.e., earth to satellite(s)), an earth-orbiting satellite receiving and transmitting portion, and a downlink portion (i.e., satellite(s) to earth).
In dwellings that receive signals from a satellite broadcast system, signal receiving equipment may be used to frequency shift the entire broadcast spectrum of the satellite(s), and frequency stack the resultant output onto a single coaxial cable. However, as the number of satellites within a satellite broadcast system increases, and with the proliferation of high definition satellite channels, a point will be reached where the total bandwidth required to accommodate all of the satellites will exceed the transmission capability of the coaxial cable. It has become necessary for the satellite decoder industry to implement more satellite slots into their distribution systems. To provide for the increased number of satellite slot transmissions a more elaborate means for satellite configurations selection is required. The two primary methods, used now for selecting these various configurations are the legacy LNB power supply method and the new Frequency Translation Module (SWM) method.
The legacy LNB power supply method controls satellite RF tone on or off selection by voltage level and a superimposed, 600 mvp-p, 22 kHz tone. Tone selection is accomplished by either a constant tone or a Pulse Width Modulated (PWM) tone. The industry standard for the PWM tone is called DiSEqC and is defined in the Eutelsat DiSEqC Bus Functional Specification. The two stage, output voltage (13 or 18 volts) is typically used to select the polarity of incoming satellite signals and the tone selects various satellite slots in space.
The second method (SWM) is self powered, therefore, it does not require an LNB power supply, and uses a UART controlled 2.3 MHz, Frequency Shift Key (FSK) modulation scheme to communicate selection commands to the satellite configuration switch. Other modulation methods may be substituted for the UART modulation method. The SWM switch is designed to select a satellite signal transponder from a host of satellite receiver antennas and translate it, in frequency, to a single transponder. This new frequency shifted transponder band is then sent to the satellite decoder box through the connecting coax cable.
Present day satellite decoder systems need the ability to switch between these two communication methods and operate in either mode without being disturbed by the other system. If a satellite receiver system is capable of SWM operation, the conventional LNB power supply will be disabled such that all control and selection of the available satellite signals is done with the modulated 2.3 MHz, SWM communication channel.
However, a problem arises when multiple circuits are coupled to the RF conductor of the coaxial cable where each circuit is required to perform a different task. For example, the SWM requires the outdoor unit to 20V power supply to co-exist with the 2.3 MHz tone on the same RF cable. The low impedance of the 20V DC power supply may short the 2.3 MHz tone to ground and result in 2.3 MHz SWM failure. Furthermore, some current satellite systems required the 5 MHz to 30 MHz band to be reserved for home networking use. The low impedance of the 20 volt power supply will also short this frequency band to ground.
An additional concern arises in that the 2.3 MHz SWM tone could cause harmonics to arise on the shared RF cable. These harmonics may interrupt other working systems on the shared RF cable. The 2.3 MHz SWM tone can be as high as 0.7 volts. If such a voltage is applied on surge protection diode or a transistor b-e junction, harmonic could occur on the RF coax cable and affects other working unit on same conductor.
Additionally, all the circuitry of the SWM system must be protected from voltage and current surges generated by environmental conditions, such as lightning. The SWM system must coexist with this surge protection and harmonic cancellation circuitry. Thus, it is desirable to have a circuit which can withstand high surge and has low capacitance to ground without disturbing the RF program signals, the SWM tone or DC supply voltages while addressing the above stated problems. The present invention described herein addresses these and/or other problems that presently exist.